SymmetricAlgorithm Class
[ This article is for Windows Phone 8 developers. If you’re developing for Windows 10, see the latest documentation. ]
Represents the abstract base class from which all implementations of symmetric algorithms must inherit.
Assembly: mscorlib (in mscorlib.dll)
The SymmetricAlgorithm type exposes the following members.
| Name | Description | |
|---|---|---|
 | BlockSize | Gets or sets the block size, in bits, of the cryptographic operation. |
| IV | Gets or sets the initialization vector (IV) for the symmetric algorithm. |
| Key | Gets or sets the secret key for the symmetric algorithm. |
| KeySize | Gets or sets the size, in bits, of the secret key used by the symmetric algorithm. |
| LegalBlockSizes | Gets the block sizes, in bits, that are supported by the symmetric algorithm. |
| LegalKeySizes | Gets the key sizes, in bits, that are supported by the symmetric algorithm. |
| Name | Description | |
|---|---|---|
 | Clear | Releases all resources used by the SymmetricAlgorithm class. |
| CreateDecryptor() | Creates a symmetric decryptor object with the current Key property and initialization vector (IV). |
| CreateDecryptor(array<Byte>, array<Byte>) | When overridden in a derived class, creates a symmetric decryptor object with the specified Key property and initialization vector (IV). |
| CreateEncryptor() | Creates a symmetric encryptor object with the current Key property and initialization vector (IV). |
| CreateEncryptor(array<Byte>, array<Byte>) | When overridden in a derived class, creates a symmetric encryptor object with the specified Key property and initialization vector (IV). |
 | Dispose | Releases the unmanaged resources used by the SymmetricAlgorithm and optionally releases the managed resources. |
| Equals(Object) | Determines whether the specified Object is equal to the current Object. (Inherited from Object.) |
| Finalize | Allows an object to try to free resources and perform other cleanup operations before the Object is reclaimed by garbage collection. (Inherited from Object.) |
| GenerateIV | When overridden in a derived class, generates a random initialization vector (IV) to use for the algorithm. |
| GenerateKey | When overridden in a derived class, generates a random key (Key) to use for the algorithm. |
| GetHashCode | Serves as a hash function for a particular type. (Inherited from Object.) |
| GetType | Gets the Type of the current instance. (Inherited from Object.) |
| MemberwiseClone | Creates a shallow copy of the current Object. (Inherited from Object.) |
| ToString | Returns a string that represents the current object. (Inherited from Object.) |
| ValidKeySize | Determines whether the specified key size is valid for the current algorithm. |
| Name | Description | |
|---|---|---|
 | BlockSizeValue | Represents the block size, in bits, of the cryptographic operation. |
| IVValue | Represents the initialization vector (IV) for the symmetric algorithm. |
| KeySizeValue | Represents the size, in bits, of the secret key used by the symmetric algorithm. |
| KeyValue | Represents the secret key for the symmetric algorithm. |
| LegalBlockSizesValue | Specifies the block sizes, in bits, that are supported by the symmetric algorithm. |
| LegalKeySizesValue | Specifies the key sizes, in bits, that are supported by the symmetric algorithm. |
| Name | Description | |
|---|---|---|
  | IDisposable::Dispose | Infrastructure. Releases the unmanaged resources used by the SymmetricAlgorithm and optionally releases the managed resources. |
The classes that derive from the SymmetricAlgorithm class use a chaining mode called cipher block chaining (CBC), which requires a key (Key) and an initialization vector (IV) to perform cryptographic transformations on data. To decrypt data that was encrypted using one of the SymmetricAlgorithm classes, you must set the Key property and the IV property to the same values that were used for encryption. For a symmetric algorithm to be useful, the secret key must be known only to the sender and the receiver.
AesManaged is an implementation of the SymmetricAlgorithm class.
Note that when using derived classes, it is not enough, from a security perspective, to simply force a garbage collection after you have finished using the object. You must explicitly call the Clear method on the object to zero out any sensitive data within the object before it is released. Note that garbage collection does not zero out the contents of collected objects but simply marks the memory as available for reallocation. Thus the data contained within a garbage collected object may still be present in the memory heap in unallocated memory. In the case of cryptographic objects, this data could contain sensitive information such as key data or a block of plain text.
All cryptographic classes in the .NET Framework that hold sensitive data implement a Clear method. When called, the Clear method overwrites all sensitive data within the object with zeros and then releases the object so that it can be safely garbage collected. When the object has been zeroed and released, you should then call the Dispose method with the disposing parameter set to True to dispose of all managed and unmanaged resources associated with the object.
Notes to InheritorsWhen you inherit from the SymmetricAlgorithm class, you must override the following members: CreateDecryptor, CreateEncryptor, GenerateIV, and GenerateKey.